Plasma vasopressin,renin activity,and aldosterone responses to maximal exercise in active college females

Summary The effect of maximal treadmill exercise on plasma concentrations of vasopressin (AVP); renin activity (PRA); and aldosterone (ALDO) was studied in nine female college basketball players before and after a 5-month basketball season. Pre-season plasma AVP increased (p<0.05) from a pre-exercise concentration of 3.8±0.5 to 15.8±4.8 pg · ml⁻¹ following exercise. Post-season, the pre-exercise plasma AVP level averaged 1.5±0.5 pg · ml⁻¹ and increased to 16.7±5.9 pg · ml⁻¹ after the exercise test. PRA increased (p<0.05) from a pre-exercise value of 1.6±0.6 to 6.8±1.7 ngAI · ml⁻¹ · hr⁻¹ 5 min after the end of exercise during the pre-season test. In the post-season, the pre-exercise PRA was comparable (2.4±0.6 ngAI · ml⁻¹ · hr⁻¹), as was the elevation found after maximal exercise (8.3±1.9 ngAI · ml⁻¹ · hr⁻¹). Pre-season plasma ALDO increased (p<0.05) from 102.9±30.8 pg · ml⁻¹ in the pre-exercise period to 453.8±54.8 pg · ml⁻¹ after the exercise test. In the post-season the values were 108.9±19.4 and 365.9±64.4 pg · ml⁻¹, respectively. Thus, maximal exercise in females produced significant increases in plasma AVP, renin activity, and ALDO that are comparable to those reported previously for male subjects. Moreover, this response is remarkably reproducible as demonstrated by the results of the two tests performed 5 months apart.     

Atrial natriuretic peptide response to endurance physical training in the rat

Summary The effect of an endurance physical training programme on the plasma and atrial natriuretic peptides (ANP) and on renal glomerular ANP receptors was evaluated in male normotensive Wistar rats. Maximal O₂ uptake was significantly greater in the endurance trained (117.1 Ml O₂ · kg^–1 · min^–1, SEM 6.18 versus the control rats 84.2 ml O₂ · kg^–1 · min^–1, SEM 4.88, P<0.01. In addition, various muscle oxidative enzymes were also significantly higher in endurance trained animals. An increase in resting plasma [ANP] was observed after 11 weeks of physical training (40.02 pg · ml^–1, SEM 7.07 vs 22.8 pg.ml^–1, SEM 3.83, P<0.05). Glomerular ANP receptor density was lower in trained rats (272 fmol · mg^–1 protein, SEM 3.1 vs 380 fmol · mg^–1 protein, SEM 6.1, P < 0.05), whereas atrial tissue [ANP] was not significantly different between controls and trained animals. However, in trained rats, circulating [ANP] was closely correlated with left atrial [ANP] (r = –0.92, P<0.05). Resting systolic blood pressure had not changed at the end of this physical training programme. It is considered that under physiological conditions ANP may be involved in long-term extracellular fluid volume homeostasis through the regulation of renal glomerular ANP receptors, and that the left atrium might play a significant role in this long term fluid volume control.     

Strenuous endurance training in humans reduces oxidative stress following exhausting exercise

The aim of this study was to evaluate whether high-intensity endurance training would alleviate exercise-induced oxidative stress. Nine untrained male subjects (aged 19–21 years) participated in a 12-week training programme, and performed an acute period of exhausting exercise on a cycle ergometer before and after training. The training programme consisted of running at 80% maximal exercise heart rate for 60 min · day⁻¹, 5 days · week⁻¹ for 12 weeks. Blood samples were collected at rest and immediately after exhausting exercise for measurements of indices of oxidative stress, and antioxidant enzyme activities [superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT)] in the erythrocytes. Maximal oxygen uptake (V˙O_2max) increased significantly (P < 0.001) after training, indicating an improvement in aerobic capacity. A period of exhausting exercise caused an increase (P < 0.01) in the ability to produce neutrophil superoxide anion (O₂ ^•−) both before and after endurance training, but the magnitude of the increase was smaller after training (P < 0.05). There was a significant increase in lipid peroxidation in the erythrocyte membrane, but not in oxidative protein, after exhausting exercise, however training attenuated this effect. At rest, SOD and GPX activities were increased after training. However, there was no evidence that exhausting exercise enhanced the levels of any antioxidant enzyme activity. The CAT activity was unchanged either by training or by exhausting exercise. These results indicate that high-intensity endurance training can elevate antioxidant enzyme activities in erythrocytes, and decrease neutrophil O₂ ^•− production in response to exhausting exercise. Furthermore, this up-regulation in antioxidant defences was accompanied by a reduction in exercise-induced lipid peroxidation in erythrocyte membrane. Accepted: 26 September 2000     

Levels of serum creatine kinase and myoglobin in women after two isometric exercise conditions

Summary The purpose of this study was to measure serum creatine kinase (CK) activity and serum myoglobin (MG) concentrations in women after two unilateral isometric knee extension exercises. Forty maximal voluntary contractions (MVC) were held for 10 s, with either a 5 s (10∶5) or 20 s 10∶20 exercise (349.4±66.1 mU · ml⁻¹) and 6 h and MG values were measured pre, 0, 3, 6, and 18 h post exercise. For CK, the highest post exercise values were observed at 6 h following the 10∶20 exercise (349.4±66.1 mU · ml⁻¹) and 6 h following the 10∶5 exercise (194.1±18.6 mU · ml⁻¹). For MG, the highest values were found 3 h after the 10∶20 exercise (148.9±61.7 ng · ml⁻¹) and 6 h after the 10∶5 exercise (67.3±10.9 ng · ml⁻¹). Serum CK and MG levels were significantly greater (p<0.01) after the 10∶20 exercise bout. The data demonstrate that CK and MG values for women increase significantly after isometric exercise. Since greater tension levels were maintained during the 10∶20 exercise it is hypothesized that increased serum CK and MG values after isometric exercise may be related to the tension generated by the contracting muscle.     

Effects of angiotensin II on arterial pressure,renin and aldosterone during exercise

Summary To evaluate the effect of isotonic exercise on the response to angiotensin II, angiotensin II in saline solution was infused intravenously (7.5 ng · kg⁻¹ · min⁻¹) in seven normal sodium replete male volunteers before, during and after a graded uninterrupted exercise test on the bicycle ergometer until exhaustion. The subjects performed a similar exercise test on another day under randomized conditions when saline solution only was infused. At rest in recumbency angiotensin II infusion increased plasma angiotensin II from 17 to 162 pg · ml⁻¹ (P<0.001). When the tests with and without angiotensin II are compared, the difference in plasma angiotensin II throughout the experiment ranged from 86 to 145 pg · ml⁻¹. The difference in mean intra-arterial pressure averaged 17 mmHg at recumbent rest, 12 mmHg in the sitting position, 9 mmHg at 10% of peak work rate and declined progressively throughout the exercise test to become non-significant at the higher levels of activity. Plasma renin activity rose with increasing levels of activity but angiotensin II significantly reduced the increase. Plasma aldosterone, only measured at rest and at peak exercise, was higher during angiotensin II infusion; the difference in plasma aldosterone was significant at rest, but not at peak exercise. In conclusion, the exercise-induced elevation of angiotensin II does not appear to be an important factor in the increase of blood pressure. It is suggested that the vasodilating mechanisms in the working muscles and the vasoconstricting mechanisms in the non-working vascular beds are powerful and dominant during isotonic exercise and attenuate the opposing or additive vasoconstrictor effects of angiotensin II. The negative feedback effect of angiotensin II on renal renin secretion, however, is not inhibited by exercise.     

Physiological and metabolic responses of female games and endurance athletes to prolonged, intermittent, high-intensity running at 30° and 16°C ambient temperatures

Eight female games players (GP) and eight female endurance athletes (EA) ran intermittently at high-intensity and for prolonged periods in hot (30°C) and moderate (16°C) ambient temperatures. The subjects performed a two-part (A, B) test based on repeated 20-m shuttle runs. Part A comprised 60 m of walking, a maximal 15-m sprint, 60 m of cruising (90% maximal oxygen uptake, V˙O_2max) and 60 m of jogging (45% V˙O_2max) repeated for 75 min with a 3-min rest every 15 min. Part B involved an exercise and rest pattern of 60-s running at 100% V˙O_2max and 60-s rest which was continued until fatigue. Although the GP and EA did not respond differently in terms of distances completed, performance was 25 (SEM 4)% less (main effect trial, P < 0.01) in the hot (HT) compared with the moderate trial (MT). Sprints of 15 m took longer to complete in the heat (main effect, trial, P < 0.01), and sprint performance declined during HT but not MT (interaction, trial × time, P < 0.01). A very high correlation was found between the rate of rise in rectal temperature in HT and the distance completed [GP, r =−0.94, P < 0.01; EA (n = 7), r = −0.93, P < 0.01]. Blood lactate [La⁻ ]_b and plasma ammonia [NH₃]_p1 concentrations were higher for GP than EA, but were similar in HT and MT [La⁻ ]_b, HT: GP vs EA, 8.0 (SEM 0.9) vs 4.9 (SEM 1.1) mmol · l⁻¹; MT: GP vs EA, 8.0 (SEM 1.3) vs 4.4 (SEM 1.2) mmol · l⁻¹; interaction, group × time, P < 0.01; [NH₃]_p1, HT: GP vs EA, 70.1 (SEM 12.7) vs 43.2 (SEM 6.1) mmol · l⁻¹; MT: GP vs EA, 76.8 (SEM 8.8) vs 32.5 (SEM 3.8) μmol · l⁻¹; interaction, group × time, P < 0.01. Ad libitum water consumption was higher in HT [HT: GP vs EA, 18.9 (SEM 2.9) vs 13.5 (SEM 1.7) ml · kg⁻¹ · h⁻¹; MT: GP vs EA, 12.7 (SEM 3.7) vs 8.5 (SEM 1.5) ml · kg⁻¹ · h⁻¹; main effect, group, n.s.; main effect, trial, P < 0.01]. These results would suggest that elevated body temperature is probably the key factor limiting performance of prolonged, intermittent, high-intensity running when the ambient temperature is high, but not because of its effect on the metabolic responses to exercise. Accepted: 19 July 1999     

Effects of inducing physiological hyperglucagonemia on metabolic responses to exercise

The purpose of the present study was to assess the effects of exogenously increasing the circulating levels of glucagon on the metabolic responses to exercise in rats. A total of six groups of rats were infused (iv) either with glucagon (20 or 50 ng·kg⁻¹·min⁻¹) or saline (0.9% NaCl), either in the resting state or during a bout of running exercise (45 min, 26 m·min⁻¹, 0% grade). Blood samples were taken at the end of the 45-min experiment. Animals infused with glucagon at 50 ng·kg⁻¹·min⁻¹ showed significantly (P<0.01) higher mean plasma glucagon concentrations than animals infused with saline or glucagon at 20 ng·kg⁻¹·min⁻¹. In addition, exercise resulted in significantly (P<0.05) higher mean plasma glucagon concentrations, compared to rest, in all groups. In spite of these differences in glucagon concentrations, there were no significant (P>0.05) effects of exercise and glucagon infusion on mean hepatic glycogen, plasma glucose, insulin, C-peptide, β-hydroxybutyrate, or catecholamine concentrations. Although exercise resulted in a significant (P<0.01) increase in plasma glycerol and free fatty acid concentrations and a significant (P<0.05) decrease in glycogen in the soleus muscle, these responses were not affected by the glucagon infusion. These results suggest that the liver is non-responsive to physiological hyperglucagonemia in a short-term (45 min) exercise situation. Electronic Publication     

Blood metabolite and catecholamine responses to prolonged exercise following either acute plasma volume expansion or short-term training

 To determine the effect of acute plasma volume (PV) expansion on substrate utilization, blood metabolites and catecholamines to prolonged, moderate intensity cycle exercise, eight untrained men mean maximal oxygen uptake,O_2max 4.10 (SEM 0.32) l · min⁻¹ were infused (10 ml·kg⁻¹) with a 6% dextran (DEX) solution. These responses were also compared to those elicited using a short-term training (TR) protocol involving cycling for 90 to 120 min · day⁻¹ at 60% O_2max for 3 consecutive days. In general DEX, which resulted in a calculated expansion of PV by 23.9%, was without effect in modifying exercise oxygen uptake or the reduction in the respiratory exchange ratio (R) observed during prolonged exercise. In addition, the concentrations of blood glucose, glycerol, alanine and serum free fatty acids, although altered (P < 0.05) by exercise, were not altered by DEX. Blood lactate concentration was only higher (P < 0.05) at 30 min of exercise during DEX compared to the control. With the exception of blood lactate concentration, which was reduced (P < 0.05), TR did not change R or the concentrations of other blood metabolites. The concentrations of nonadrenaline and adrenaline, were depressed (P < 0.05) by DEX and TR at 60 and 90 min of exercise. These results would suggest that mechanisms as yet undefined can compensate for the estimated 10% reduction in arterial oxygen content mediated by acute PV expansion and enable prolonged exercise to be performed without adjustments in substrate selection and substrate mobilization. Accepted: 23 August 1996     

Enhancement of the finger cold-induced vasodilation response with exercise training

Cold-induced vasodilatation (CIVD) is a cyclical increase in finger temperature that has been suggested to provide cryoprotective function during cold exposures. Physical fitness has been suggested as a potential factor that could affect CIVD response, possibly via central (increased cardiac output, decreased sympathetic nerve activity) and/or peripheral (increased microcirculation) cardiovascular and neural adaptations to exercise training. Therefore, the purpose of this study was to investigate the effect of endurance exercise training on the CIVD response. Eighteen healthy males trained 1 h d⁻¹ on a cycle ergometer at 50% of peak power output, 5 days week⁻¹ for 4-weeks. Pre, Mid, Post, and 10 days after the cessation of training and on separate days, subjects performed an incremental exercise test to exhaustion (\mathop V ^· \textO_2\textpeak ), (\mathop V\limits^{ \cdot }\!\! {\text{O}}_{{2{\text{peak}}}} ), and a 30-min hand immersion in 8°C water to examine their CIVD response. The exercise-training regimen significantly increased \mathop V ^·\textO_2\textpeak \mathop V\limits^{ \cdot }\!\!{\text{O}}_{{2{\text{peak}}}} (Pre: 46.0 ± 5.9, Mid: 52.5 ± 5.7, Post: 52.1 ± 6.2, After: 52.6 ± 7.6 ml kg⁻¹ min⁻¹; P < 0.001). There was a significant increase in average finger skin temperature (Pre: 11.9 ± 2.4, After: 13.5 ± 2.5°C; P < 0.05), the number of waves (Pre: 1.1 ± 1.0, After: 1.7 ± 1.1; P < 0.001) and the thermal sensation (Pre: 1.7 ± 0.9, After: 2.5 ± 1.4; P < 0.001), after training. In conclusion, the aforementioned endurance exercise training significantly improved the finger CIVD response during cold-water hand immersion.     

Effects of physical exercise and anti-G suit inflation on atrial natriuretic factor plasma level

Summary The purpose of this study was to measure the effect of enhanced venous return on atrial natriuretic factor (ANF) secretion during exercise and upright posture and the consequences on renin angiotensin aldosterone system (RAAS) activity. Six healthy male subjects were submitted to four different procedures. All procedures were performed in the same position, i.e. riding on a support with legs hanging. Two procedures were performed at rest: the subjects were studied after a 25-min rest in this position, with and without the lower limb fitted with an anti-G suit inflated to 60 mmHg. Two procedures were carried out with physical exercise; arm-cranking was performed in the same position with and without the anti-G suit inflated to 60 mmHg. Venous blood was collected before and after each procedure in order to measure plasma ANF, plasma aldosterone concentration (PAC), plasma renin activity (PRA), corticotrophin (ACTH) and catecholamine level. The data mean ±SEM showed that the ANF plasma level decreased significantly (p<0.05) from 32.5±4 to 28±6 pg · ml⁻¹ after a 20-min rest in the upright posture, whereas this effect was absolished with anti-G suit inflation. Physical exercise with and without the anti-G suit increased the ANF level above control values (60±13.6 pg · ml⁻¹ and 53±13 pg · ml⁻¹): anti-G suit inflation had no significant effect. PRA increased after rest in an upright posture and during physical exercise; anti-G suit inflation abolished this increase in both conditions. PAC was not influenced by postural change but significantly increased in all exercise tests. ACTH increased to the same extent in both exercise tests. The plasma catecholamine level increased during upright posture and both physical exercise procedures. These results indiate that enhanced venous return during anti-G suit inflation increases ANF secretion at rest in an upright posture and that physical exercise greatly increases plasma ANF level independently of the anti-G suit inflation. They suggest that ANF release during exercise could be influenced by factors other than haemodynamic stimuli. The comparison between ANF and PRA changes during arm-cranking indicates that PRA is influenced more than ANF by blood volume displacement. The ANF increase during exercise does not inhibit aldosterone secretion.     

Plasma norepinephrine and heart rate dynamics during recovery from submaximal exercise in man

Summary The time course of heart rate (HR) and venous blood norepinephrine concentration [NE], as an expression of the sympathetic nervous activity (SNA), was studied in six sedentary young men during recovery from three periods of cycle ergometer exercise at 21%±2.8%, 43%±2.1% and 65%±2.3% of respectively (mean±SE). The HR decreased mono-exponentially withτ values of 13.6±1.6 s, 32.7±5.6 s and 55.8±8.1s respectively in the three periods of exercise. At the low exercise level no change in [NE] was found. At medium and high exercise intensity: (a) [NE] increased significantly at the 5th min of exercise (Δ[NE]=207.7±22.5 pg·ml⁻¹ and 521.3±58.3 pg·ml⁻¹ respectively); (b) after a time lag of 1 min [NE] decreased exponentially (τ=87 s and 101 s respectively); (c) in the 1st min HR decreased about 35 beats · min⁻¹; (d) from the 2nd to 5th min of recovery HR and [NE] were linearly related (100 pg·ml⁻¹ Δ[NE]5 beats ·min⁻¹). In the 1st min of recovery, independent of the exercise intensity, the adjustment of HR appears to have been due mainly to the prompt restoration of vagal tone. The further decrease in HR toward the resting value could then be attributed to the return of SNA to the pre-exercise level.     

Diurnal variation in the salivary melatonin responses to exercise: relation to exercise-mediated tachycardia

Salivary melatonin concentration is an established marker of human circadian rhythmicity. It is thought that melatonin is relatively robust to the masking effects of exercise. Nevertheless, the extent and even the direction of exercise-related change is unclear, possibly due to between-study differences in the time of day exercise is completed. Therefore, we aimed to compare melatonin responses between morning and afternoon exercise, and explore the relationships between exercise-related changes in melatonin and heart rate. At 08:00 and 17:00 hours, seven male subjects (mean ± SD age, 27 ± 5 years) completed 30 min of cycling at 70% peak oxygen uptake followed by 30 min of rest. Light intensity was maintained at ~150 lx. Salivary melatonin (ELISA) and heart rate were measured at baseline, 15 min during exercise, immediately post-exercise and following 30 min recovery. Melatonin was ≈15 pg ml⁻¹ higher in the morning trials compared with the afternoon (P = 0.030). The exercise-related increase in melatonin was more pronounced (P = 0.024) in the morning (11.1 ± 8.7 pg ml⁻¹) than in the afternoon (5.1 ± 5.7 pg ml⁻¹). The slope of the heart rate–melatonin relationship was significantly (P = 0.020) steeper in the morning (0.12 pg ml⁻¹ beats⁻¹ min⁻¹) than in the afternoon (0.03 pg ml⁻¹ beats⁻¹ min⁻¹). In conclusion, we report for the first time that the masking effect of moderate-intensity exercise on melatonin is approximately twice as high in the morning than the afternoon. The much steeper relationship between heart rate and melatonin changes in the morning raises the possibility that time of day alters the relationships between exercise-mediated sympathetic nervous activity and melatonin secretion.     

Saliva flow and composition in humans exposed to acute altitude hypoxia

Summary The effects of acute hypoxia (2 days at 4350 m) on whole saliva flow and composition were studied on 12 sea-level natives, at rest and following a maximal exercise. Exercise, performed in normoxia and hypoxia, did not induce variations in saliva flow rate, saliva potassium or α-amylase concentrations. In contrast, acute hypoxia did lead to an increase in mean saliva flow rate both at rest (0.63 ml·min⁻¹ to 0.93 ml·min⁻¹,P<0.01) and after exercise (0.56 ml·min⁻¹ to 1.06 ml·min⁻¹,P<0.05) and a decrease in mean saliva potassium concentration at rest (20.8 mmol·1⁻¹ to 14.7 mmol·1⁻¹,P<0.01) as well as after exercise (21.7 mmol·1⁻¹ to 16.5 mmol·1⁻¹,P<0.05). This effect might be the consequence of a hypoxia-induced stimulation of the parasympathetic nervous system.     

Maximal voluntary hyperpnoea increases blood lactate concentration during exercise

Ventilatory work during heavy endurance exercise has not been thought to influence systemic lactate concentration. We evaluated the effect of maximal isocapnic volitional hyperpnoea upon arterialised venous blood lactate concentration ([lac⁻]_B) during leg cycling exercise at maximum lactate steady state (MLSS). Seven healthy males performed a lactate minimum test to estimate MLSS, which was then resolved using separate 30 min constant power tests (MLSS=207±8 W, mean ± SEM). Thereafter, a 30 min control trial at MLSS was performed. In a further experimental trial, the control trial was mimicked except that from 20 to 28 min maximal isocapnic volitional hyperpnoea was superimposed on exercise. Over 20–28 min minute ventilation, oxygen uptake, and heart rate during the control and experimental trials were 87.3±2.4 and 168.3±7.0 l min⁻¹ (P<0.01), the latter being comparable to that achieved in the maximal phase of the lactate minimum test (171.9±6.8 l min⁻¹), 3.46±0.20 and 3.83 ± 0.20 l min⁻¹ (P<0.01), and 158.5±2.7 and 166.8±2.7 beats min⁻¹ (P<0.05), respectively. From 20 to 30 min of the experimental trial [lac⁻]_B increased from 3.7±0.2 to 4.7±0.3 mmol l⁻¹ (P<0.05). The partial pressure of carbon dioxide in arterialised venous blood increased approximately 3 mmHg during volitional hyperpnoea, which may have attenuated the [lac⁻]_B increase. These results show that, during heavy exercise, respiratory muscle work may affect [lac⁻]_B. We speculate that the changes observed were related to the altered lactate turnover in respiratory muscles, locomotor muscles, or both.     

Beta-endorphin immunoreactivity during high-intensity exercise with and without opiate blockade

Nine highly fit men [mean (SE) maximum oxygen uptake, : 63.9 (1.7) ml·kg^–1·min^–1; age 27.6 (1.6) years] were studied during two treadmill exercise trials to determine plasma β-endorphin immunoreactivity during intense exercise (80% ). A double-blind experimental design was used, and subjects performed the two exercise trials in counterbalanced order. Exercise trials were 30 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration of naloxone (1.2 mg; 3 cm³) and the other after receiving a placebo (0.9% NaCl saline; 3 cm³). Prior to each experimental trial, a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Thereafter, each subject received either a naloxone or placebo bolus injection. Blood samples were also collected after 10, 20 and 30 min of continuous exercise. β-Endorphin was higher (P<0.05) during exercise when compared to pre-exercise in both trials. However, no statistically significant difference was found (P>0.05) between exercise time points within either experimental trial. β-endorphin immunoreactivity was greater (P<0.05) in the naloxone than in the placebo trial during each exercise sampling time point [10 min: 63.7 (3.9) pg·ml^–1 vs 78.7 (3.8) pg·ml^–1; 20 min: 68.7 (4.1) pg·ml^–1 vs 83.8 (4.3) pg·ml^–1; 30 min: 71.0 (4.3) pg·ml^–1 vs 82.5 (3.2) pg·ml^–1]. These data suggest that intense exercise induces significant increases in β-endorphin that are maintained over time during steady-rate exercise. Exercise and naloxone had an interactive effect on β-endorphin release that warrants further investigation. Electronic Publication     

Cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise

In occupational work, continuous repetitive and isometric actions performed with the upper extremity primarily cause local muscle strain and musculoskeletal disorders. They may also have some adverse effects on the cardiorespiratory system, particularly, through the elevation of blood pressure. The aim of the present study was to compare peak cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise. The subjects were 21 untrained healthy men aged 24–45 years. The dynamic hand-grip exercise (DHGE) was performed using the left hand-grip muscles at the 57 (SD 4)% level of each individual's maximal voluntary contraction (MVC) with a frequency of 51 (SD 4) grips · min^−l. The isometric hand-grip exercise (IHGE) was done using the right hand at 46 (SD 3)% of the MVC. The endurance time, ventilatory gas exchange, heart rate (HR) and blood pressure were mea- sured during both kinds of exercise. The mean endurance times for DHGE and IHGE were different, 170 (SD 62) and 99 (SD 27) s, respectively (P < 0.001). During DHGE the mean peak values of the breathing frequency [20 (SD 6) breaths · min⁻¹] and tidal volume [0.89 (SD 0.34) l] differed significantly (P < 0.01) from peak values obtained during IHGE [15 (SD 5) breaths · min⁻¹, and 1.14 (SD 0.32) l, respectively]. The corresponding peak oxygen consumptions, pulmonary ventilations, HR and systolic blood pressures did not differ, and were 0.51 (SD 0.06) and 0.46 (SD 0.11) l · min⁻¹, 17.1 (SD 3.0) and 16.7 (SD 4.7) l · min⁻¹, 103 (SD 18) and 102 (SD 17) beats · min⁻¹, and 156 (SD 17) and 161 (SD 17) mmHg, respectively. The endurance times of both DHGE and IHGE were short (<240 s). The results indicate that the peak responses for the ventilatory gas exchange, HR and blood pressure were similar during fatiguing DHGE and IHGE, whereas the breathing patterns differed significantly between the two types of exercise. The present findings emphasize the importance of following ergonomic design principles in occupational settings which aim to reduce the output of force, particularly in tasks requiring isometric and/or one-sided repetitive muscle actions. Accepted: 16 February 2000     

Metabolic profile of 4 h cycling in the field with varying amounts of carbohydrate supply

Several laboratory studies have demonstrated a performance-enhancing effect of carbohydrate (CHO) supplementations during endurance sessions of long duration. However, the transferability of these results to real training and competition circumstances has not been conclusively shown. Therefore, we tried to test the influence of graded CHO substitution on substrate utilization and selected physiological parameters under standardized but practically orientated field conditions. Fourteen endurance-trained male subjects [mean (SD): 25 (5) years, 72 (9) kg, V˙O_2max 67 (6) ml·min^–1·kg^–1, individual anaerobic threshold (IAT) 269 (30) W] after a stepwise increasing pre-test had to perform three 4-h endurance rides on their own bicycles with simultaneous spiroergometry: constant workload 70% IAT (monitoring by SRM-System). Before and during exercise, solutions without (0%), with 6% or 12% CHO were administered double-blindly and in randomized order (total volume: 50 ml·kg^–1). After cessation of exercise, significant differences between 0% and both CHO concentrations were detected for blood glucose (GLU; 75 mg dl^–1 for 0% vs 101 mg dl^–1 for 6% vs 115 mg dl^–1 for 12%; P<0.001) and respiratory exchange ratio (0.84 vs 0.88 vs 0.90; P<0.01; correlation to GLU: r=0.46, P<0.05). Free fatty acids (0.19 vs 0.16 vs 0.10 mmol l^–1) and glycerol (0.41 vs 0.22 vs 0.12 mmol l^–1) were significantly different between the endurance trials in a dose-dependent manner (both P<0.001). Lactate concentration (P=0.42) and heart rate (P=0.12) had no significant influence from CHO substitution. We conclude that CHO substitution during 4-h endurance training inhibits lipolysis in a dose-dependent manner and enhances aerobic glycolysis. This proves that earlier laboratory findings can be replicated under field conditions using modern portable equipment. Electronic Publication     

Effect of strenuous strength training on the Na-K pump concentration in skeletal muscle of well-trained men

This study examined how strenuous strength training affected the Na-K pump concentration in the knee extensor muscle of well-trained men and whether leg muscle strength and endurance was related to the pump concentration. First, the pump concentration, taken as ³H-ouabain binding, was measured in top alpine skiers since strength training is important to them. Second, well-trained subjects carried out strenuous eccentric resistance training either 1, 2, or 3 times · week⁻¹ for 3 months. The Na-K pump concentration, the maximal muscle strength in a full squat lift (one repetition maximum, 1 RM), and the muscle endurance, taken as the number of full squat lifts of a mass of 70% of the 1 RM load, were measured before and after the training period. The mean pump concentration of the alpine skiers was 425 (SEM 11) nmol · kg⁻¹ wet muscle mass. The subjects in part two increased their maximal strength in a dose-dependent manner. The muscle endurance increased for all subjects but independently of the training programme. From a mean starting value of 356 (SEM 6) nmol · kg⁻¹ the mean Na-K pump concentration increased by 54 (SEM 15) nmol · kg⁻¹ (+15%, P < 0.001) when the results for all subjects were pooled. The effect was larger for those who had trained twice a week than for those who had trained only once a week (P=0.025), suggesting that the effect of strength training depended on the amount of training carried out. The muscle strength and endurance were not related to the pump concentration, suggesting that the pumping power of this enzyme did not limit the performance during heavy lifting. However, the individual improvements in the endurance test during the training period correlated with the individual changes in the pump concentration (r _Spearman=0.5; P=0.01) which could mean that a common factor both increases the pump concentration and makes the muscles more adapted to repeated heavy lifting. Accepted: 8 August 2000     

Substrate utilisation during exercise and shivering

It is generally assumed that exercise and shivering are analogous processes with regard to substrate utilisation and that, as a consequence, exercise can be used as a model for shivering. In the present study, substrate utilisation during exercise and shivering at the same oxygen consumption (V˙O₂) were compared. Following an overnight fast, eight male subjects undertook a 2-h immersion in cold water, designed to evoke three different intensities of shivering. At least 1 week later they undertook a 2-h period of bicycle ergometry during which the exercise intensity was varied to match the V˙O₂ recorded during shivering. During both activities hepatic glucose output (HGO), the rate of glucose utilisation (Rd), blood glucose, plasma insulin, free fatty acid (FFA) and beta-hydroxybutyrate (B-HBA) concentrations were measured. The V˙O₂ measured during the different levels of shivering averaged 0.49 l · min⁻¹ (level 1: low), 0.6 l · min⁻¹ (level 2: low-moderate), and 0.9 l · min⁻¹ (level 3: moderate), and corresponded closely to the levels measured during exercise. HGO and Rd were greater (P < 0.05) during exercise than during shivering at the same V˙O₂ (9.5% and 14.7%, respectively). The average (SD) HGO during level 3 exercise was 3.0 (0.91) mg · kg⁻¹ . min⁻¹ compared to 2.76 (1.0) mg · kg⁻¹ . min⁻¹ during shivering. The values for Rd were 3.06 (0.98) mg · kg⁻¹ · min⁻¹ during level 3 exercise and 2.68 (0.82) mg · kg⁻¹ · min⁻¹ during shivering. Blood glucose levels did not differ between conditions, averaging 5.4 (0.3) mmol . l⁻¹ over all levels of shivering and 5.2 (0.3) mmol · l⁻¹ during exercise. Plasma FFA and B-HBA were higher (P < 0.01) during shivering than during corresponding exercise (12.3% and 33.3%, respectively). FFA averaged 0.61 (0.2) mmol · l⁻¹ over all levels of shivering and 0.47 (0.16) mmol · l⁻¹ during exercise. The figures for B-HBA were 0.44 (0.13) mmol · l⁻¹ during all levels of shivering and 0.32 (0.1) mmol · l⁻¹ during exercise. Plasma insulin was higher (P < 0.05) during level 2 and 3 shivering compared to corresponding exercise; at these levels the average value for plasma insulin was 95.9 (21.9) pmol · l⁻¹ during shivering and 80.6 (16.1) pmol · l⁻¹ during exercise. On the basis of the present findings it is concluded that, with regard to substrate utilisation, shivering and exercise of up to 2 h duration should not be regarded as analogous processes. Accepted: 12 February 1997     

Effect of altered pre-exercise carbohydrate availability on selection and perception of effort during prolonged cycling

This study assessed the effect of altered carbohydrate (CHO) availability on self-selected work rate during prolonged time-trial cycling. Eight endurance-trained men undertook two experimental cycling time-trials after glycogen-depleting exercise and 2 days of: (a) high (9.3 ± 0 g CHO kg⁻¹ day⁻¹) (HC) and (b) low CHO intakes (0.6 ± 0.1 g CHO kg⁻¹ day⁻¹) (LC), via a double-blinded crossover design. All feedback regarding performance was removed during both exercise trials. Self-selected external power output was not different during the first 2 h of exercise between experimental conditions (P > 0.05), despite reported sensations of increased tiredness before and during exercise, significantly reduced whole body CHO oxidation (P < 0.05), plasma lactate concentrations (P < 0.05) and earlier onset of fatigue during exercise in LC versus HC. Perceived exertion was not different throughout exercise between conditions (P > 0.05). Mean power output declined significantly in LC versus HC (P < 0.05) after ∼ 2 h of exercise, and was associated with significant reductions in cadence, heart rate and plasma glucose concentration (P < 0.05). These results demonstrate that when compared with time-trial cycling performed after a HC diet, reduced CHO availability does not initially alter self-selected work rate in endurance athletes who are deceived of their CHO status prior to exercise. This finding suggests that reduced work rate during exercise following lowered CHO intake may, in part, be a consequence of the subject’s awareness of dietary CHO restriction rather than solely a physiologically mediated action. Further research is required to distinguish the influence of circulating glucose and peripheral glycogen availability on pacing strategy during prolonged exercise.